*ahem*
I have some limited experience with LED lighting, sir.
Try this place - it's online sales only (afaik) and I just got some
4410 equivalent festoon lights from them to replace the incandescent
courtesy lights in the door steps and the cab dome light. They aren't a
perfect fit for the Chevy bulb holders, the flanges are a bit off,
but they do fit, work, and look GREAT! And they use about 1/15 the power.
Somewhere on their site there's an automotive incandescent to LED
chart, so you can figure out what you've got, and what you need to
replace it with.
http://www.superbrightleds.com/
Any more questions, email them, they're really good at LED support stuff.
Or ask markopolo. He also has some experience with LEDs.